Agriculture.

Poverty Bay Standard, Volume X, Issue 1187, 28 October 1882, Page 8 (Supplement)

Agriculture.

AGRICULTURAL DRAINAGE. By R. W. Emerson Maclvor, F.1.C.,F.C.5.,&c. AUTHOR OF “ THE CHEMISTRY OF AGRICULTURE.” The manifold advantages of artificial drainage are not recognised by many colonial settlers, who could very well afford to expend capital upon carrying it out to a much greater extent than they do. It is sure that we do not make the most of our rainfall in the less moist districts of Australia, and equally true that nothing whatever is being done by the farmers themselves to properly consume it. “We don’t want drainage, we want more rain” is not an uncommon cry. Now, it is a fact, as certain as any in science, that next to the direct storage of water, artificial drainage, effectively carried out, is the best means of giving agricultural lands the full benefit of what rainfall there may be in a naturally dry district. This should be clear from a study of the climatic circumstances of the greater part of Australia. Let us take the case of Victoria, and the arguments used, apply with as much strength to South Australia and New South Wales. In this colony the average rainfall actually exceeds that of the United Kingdom, by something over an inch, or in other.words, by .about 100 tons per acre per annum—“ If that be true,” says Ploughshare, “ where on earth does the water go to ?” Science offers • a simple explanation : — After a period of hot weather, the rain comes down on a hard, more or less sun-baked soil, and collects in pools on the surface. In a short time these pools disappear, for the most part into the air, instead of passing into the body of the earth to be there preserved for the use of growing vegetation, out of all reach of direct evaporating influences. Of a total average annual rainfall of 25 inches in Britain, about 20 inches are returned to the atmosphere by the transpiration of growing crops, and by evaporation from the surface, 5 inches or 500 tons per acre, remain to pass through the land into the drainor. In .that country the evaporating power of the air is less than the rainfall. But in Victoria these conditions are reversed; the atmosphere is capable of evaporating about 42 inches, while the total average rainfall does not much exceed 26 inches. Hence, the best step the farmer can take in order that he may preserve the rain is to so prepare his land that in place of remaining in pools on the surface, the water can readily find its way into and throughout the soil. This can be done by one means only, viz., draining. When judiciously carried out, this operation not only removes water which otherwise would stagnate on the ground until the atmosphere had taken it back to itself, but improves the porosity of the soil, and thereby facilitates the access of air, warmth and other beneficial agencies. It is better to lose part of the rainfall through drains, and conserve the remainder within the pores of the soil, than to lose, certainly, the greater part of it by superficial evaporation in the manner described. These explanations must, on reflection, convince some of our more intelligent cultivators that, whatever drainage has for its object in wet countries, its function in the drier regions of Australasia is that of a conservor of the precious fluid, without which all would be desolation and death.

In countries like New Zealand, where the rainfall is very heavy, drainage will ultimately be productive of the most beneficial results, no matter what kind of produce may be raised on the land, whether grain, root-crops, sheep, cattle, or horses. It may be true that large areas are fairly well drained by virtue of their situation, but where rushes and other aquatic vegetation blemish rich pasture or arable land by their presence, it may be taken for granted that nature has left something to be done in the direct-on of effective artificial work. As to the best kind of drain that should be adopted in a grain locality, much depends on circumstances. No material liable to perish or silt up should be used. Competent authorities agree that no channel is so effective as the cylindrical draining pipe, with or without collars. Parkes, formerly engineer to the Royal Agricultural Society of England, believed and proved that one-inch pipes were of sufficient bore for most purposes. He found that these pipes, placed 24 feet apart, were capable of carrying away 2| inches or 250 tons per acre of rain in 12 hours, a fall which, so far as the colonies are concerned, is confined to a few localities in New Zealand. It is, however, usual to employ 2 inch pipes for furrow drains, and 3 to 6 inch pipes for main or carrying drains. Good tiles should be smoothly made, free from pieces of stone, and give out a clear musical note when gently struck together. Stones about 3 inches in size or water-worn pebbles are largely used in many places, but where these are scarce the cost of carriage will induce people to adopt tiles. Professor Wrightson, a reliable authority, lays down the following general directions for the guidance of drainers:— 1. —The number of outfalls should be reduced to a minimum, as each is a source of weakness. 2. —All outfalls should be secured with a perpendicular grating, and be faced up with stone-work. 3. —Any springs should be drained off a few inches deeper than it is intended ; to drain the field generally. By following this rule, the the two systems of pipes will not interfere. 4. —Drains should be laid to intercept any water which may be expected to soak through the higher levels. 5. —Main drains should be three inches deeper than furrow drains, so that the lattei may deliver their water quickly, and prevent silting. 6. —Main drains should be provided with silting tanks, especially when the drainage works arc on a large scale. Each silting tank also to be provided with a “ man-hole,” closed with a flag and ring. 7. —The fall should not be less than 1 in 220. 8. —To avoid the accumulation of sediment, and weakening the main drain, the furrow drains should never enter a central main drain exactly opposite each other, but alternately. 9. —The greatest possible pains should be taken to arrange a plan in accordance with the levels, and to secure a good outlet.